1. Field of the Invention
The present invention relates to a method of analyzing small quantities of a nitrogen compound and a phosphorus compound which are contained in industrial waste water from a factory or the like, or environmental water such as river or lake, and an apparatus therefor.
2. Description of the Background Art
In Japan, a method of analyzing a nitrogen compound and a phosphorus compound which are contained in water is officially standardized under JIS K0102 and Notification No. 140 of the Environment Agency. A nitrogen compound which is contained in water exists in the form of nitric acid ions, nitrous acid ions, ammonium ions or organic nitrogen. While a TN (total nitrogen) analytical method of measuring total nitrogen which is contained in water is adapted to entirely convert the nitrogen compound to nitric acid ions to measure the same, it is difficult to oxidize ammonium ions and organic nitrogen into nitric acid ions. In TN measurement, therefore, an alkaline potassium peroxodisulfate solution is added to sample water, which in turn is heated at 120.degree. C. for 30 minutes so that the nitrogen compound is entirely oxidized into nitric acid ions. Then the sample water is cooled and thereafter adjusted to pH 2 to 3, to be subjected to measurement of ultraviolet absorbance by nitric acid ions at a wavelength of 220 nm.
On the other hand, a phosphorus compound which is contained in water exists in the form of phosphoric acid ions, hydrolytic phosphorus, or organic phosphorus. In TP (total phosphorus) measurement, potassium peroxodisulfate is added as an oxidizer to sample water in a neutral state, and the sample water is heated at 120.degree. C. for 30 minutes so that the phosphorus compound is entirely oxidized to phosphoric acid ions. Since phosphoric acid ions have no specific light absorption, an ammonium molybdate solution and an L-ascorbic acid solution are added as color developers to the sample water after cooling to color the same, thereby measuring absorbance at a wavelength of 880 nm.
Another TN measuring method is adapted to oxidize a nitrogen compound to nitric acid ions by an oxidation catalyst under a high temperature of at least 500.degree. C. for measuring the same as nitrogen oxides by a chemiluminescence method, or to pass nitrogen oxides further through an oxidation-reduction reaction tube at about 600.degree. C. and decompose the same to gaseous nitrogen for measuring the same as nitrogen by gas chromatography.
Still another method is adapted to supply ozone to sample water for oxidizing the same with ozone in an alkaline state in TN measurement or an acidic state in TP measurement.
There is no apparatus for analyzing TN measurement and TP measurement in sample water by a common analyzer. This is because pH conditions in oxidation with an oxidizer or ozone are different from each other such that a nitrogen compound is oxidized in an alkaline state while a phosphorus compound is oxidized in a neutral or acidic state.
In the oxidation method employing an oxidizer, sample water is heated to the high temperature of 120.degree. C. exceeding its boiling point, and hence a pressure-resistant reaction kettle is required to complicate an oxidizing apparatus in structure and operation, leading to a high cost. Further, it is necessary to frequently supply the oxidizer as consumed, leading to a high running cost.
The method of oxidizing a nitrogen compound with a catalyst requires a high temperature of at least 500.degree. C., and the catalyst is remarkably deteriorated. An apparatus therefor is complicated in structure such that the same is hard to maintain, while such an analytical method employing a catalyst is generally unsuitable for employment as a monitor on a job site.
The ozone oxidizing method requires a pH adjusting mechanism for oxidation of both nitrogen compound and phosphorus compound due to weak oxidation in a neutral area, and hence an apparatus therefor is complicated in structure. Further, acid and alkali pH adjusters are required as consumed products.
Thus, it is impossible to measure a nitrogen compound and a phosphorus compound in common by any conventional analytical method. Further, every one of the conventional methods requires a high cost and is hard to use due to insufficient fitness for a continuous monitor.
In Japan, the regulation of total emission has already been applied to organic pollutants which are contained in industrial waste water flowing into a closed sea area for the purpose of environmental protection of water quality, and COD(Chemical Oxygen Demand), TOC(Total Organic Carbon) and UV(Ultraviolet) meters are officially employed. Among these, the UV meter prevails most due to its simple structure. However, there is no apparatus for simultaneously measuring a nitrogen compound, a phosphorus compound and an organic pollutant.